Conventional magnetic recording media for horizontal recording, such as hexagonal-close-packed (HCP) cobalt-platinum (CoPt) alloys, are unable to achieve recording densities above approximately 2-5 Gbit/in.sup.2. An historic trend has been to require reduced magnetic areal moment density (M.sub.r t) and increased coercivity (H.sub.c) to achieve recording at higher recording densities. High-density recording media also need to have exchange decoupled particles or grains. Smaller grains are required at higher densities for reduced intrinsic media noise to obtain a higher signal-to-noise ratio in the readback data. Thus, high-density recording media require both a reduced M.sub.r t and a reduced grain size.
Bulk tetragonal L1.sub.0 -ordered phase materials (also called CuAu materials), such as CoPt and FePt, are known for their high magnetocrystalline anisotropy and magnetic moment, properties that are also desirable for high-density magnetic recording media. The C-axis of the L1.sub.0 phase is similar to the C-axis of HCP CoPt alloys in that both are the easy axis of magnetization. Thus, while the disordered face-centered-cubic (FCC) solid solution of Co and Pt has cubic symmetry and low magnetic anisotropy, the ordered L1.sub.0 phase has uniaxial anisotropy similar to, but greater in magnitude than, HCP CoPt alloys.
Previous studies on the L1.sub.0 phase of FePt have concentrated mainly on the epitaxial growth of highly chemically-ordered films grown by molecular beam epitaxy. Several studies dedicated to the application of sputter-deposited, chemically-ordered alloys of FePt and CoPt as thin films for horizontal magnetic recording media describe the requirement for a relatively high-temperature post-deposition annealing to achieve the chemical ordering. These are described in Coffey et al., "High Anisotropy L1.sub.0 Thin Films for Longitudinal Recording", IEEE Transactions on Magnetics, Vol. 31, No. 6, November 1995, pp. 2737-2739; and Watanabe et al., "Microstructure and Magnetic Properties of High-Coercive Fe-Pt Alloy Thin Films", Materials Transactions, JIM, Vol. 37, No. 3, 1996, pp. 489-493. This post-deposition annealing process results in an increase of the grain size from about 10 nm in the as-deposited films to about 30 nm in the annealed films. Due to this larger grain size, these films have shown rather poor recording properties, in particular a low signal-to-noise ratio. In addition, the high-temperature annealing process is not compatible with existing magnetic recording media fabrication processes and materials.
What is needed is a method for making chemically-ordered, high magnetocrystalline anisotropy FePt and CoPt thin films with a small grain size and without post-deposition annealing.